Even the most optimistic forecasters of global energy supplies are concerned about the possible adverse societal effects of energy scarcity and rationing in the foreseeable future. Unless sustainable (ie: geothermal) and renewable (ie: wind, solar) energy production grows to meet a very significant portion of global energy demand within this century, every country will be impacted by energy scarcity in the coming years. Rising fossil fuel costs driven by continuously increasing global energy demand, coupled with progressively more challenging access to reducing planetary fossil fuel reserves, not only threaten the economies of nations forced to import much of their energy, but also threaten global trade and transportation.
Due to the geographical concentration of fossil fuels, the assurance of a constant energy supply in many regions of the world relies to a very significant extent on global fossil fuel deliveries and these primarily take the form of crude oil tankers which can typically carry up to 450,000 MT of oil or coal carriers up to 400,000 MT known as Chinamax ships. Hundreds of oil tankers are constructed every year with an average size of 75,000-100,000 MT with a typical lifespan of 25 years. Upon arriving at destinations, their crude oil must be piped to refineries and the resulting products are then typically trucked to points of use—all stages consume energy and emit air pollutants and in particular, the crude oil tankers are amongst the heaviest air polluters in the world.
To prepare for future fossil fuel scarcity while also meeting hydrocarbon emission targets dictated by immediate global warming concerns, it is now common for governments to make major investments or offer significant tax incentives to spur renewable energy development (such as wind and solar, and remaining hydropower opportunities) to augment traditional sources of electrical energy (such as coal, gas and nuclear generation) and also provide financial incentives for electric ground transportation (as the growth in consumption of fossil fuels is greatest for transportation). These renewable projects often require grid upgrades and in some cases, major new transmission lines to deliver energy to consumers which equal or exceed the cost of the renewable generation facilities.
To both reduce capital costs of constructing major transmission lines, and to waste as little as possible of existing energy resources by reducing transmission losses, utilities ideally locate the production of electricity as close to major demand centers (cities, industrial complexes) as possible. For example, in the case of electrical generation via the consumption of fossil fuels and other combustibles, these feed stocks are typically shipped to generation facilities and burned as close as possible to demand centers with the downside of municipal air quality degradation. Shipping of such fossil fuels to support the electrical grid as well as home heating and transportation has grown to a global energy re-distribution industry operating thousands of ships, trains, and transport trucks.
Renewable electric energy generation (other than the combustion of ethanol and other plant-derived feed stocks) has the potential to significantly reduce further air quality degradation and ultimately to completely eliminate energy security concerns. However, as the percentage of such generation to overall electrical generation on any given continental grid grows, it poses two key challenges to distribution systems: 1) It is often not possible to locate such facilities within close proximity to demand centers; and, 2) Most renewable sources other than geothermal (which is only commercially feasible in limited areas of the planet), produce at intermittent periods which often do not coincide with demand.
The promise of a future electrical grid primarily powered by or only powered by renewable energy requires—1) an effective arrangement to locate renewable energy facilities dose to demand and 2) effective energy storage facilities capable of fulfilling energy demands irrespective of oscillating renewable energy production levels. Improved thermal energy storage can assist in providing effective solutions.
The following table, modified from “Materials Selection in Mechanical Design, 4th Edition” by Mike Ashby (Granta Design), compares energy density achievable from a variety of sources of stored energy. This table details the stored energy density—but in the case of combustible or thermal sources (Gasoline, Rocket Fuel and Thermal Graphite Storage), not what can be effectively utilised as electricity with current energy conversion methods. For example, although Gasoline's energy density is listed as 5,500 kWh/ton, when Gasoline is combusted in an internal combustion engine driving an electric generator, only a small portion of its energy potential is ultimately available as electric energy since much of the stored energy is lost in the conversion process as waste heat. Likewise, thermal energy stored in graphite must go through a conversion process to net electrical energy when used for grid support and thus, the turbine or other heat engine efficiency (typically 30-60% within such heat engine's ideal operating temperature range) determines the net energy density. Net energy from various chemical/battery storage technologies is impacted by cell life, temperature, discharge rates, and the performance of other inter-connected cells—also dropping effective output from that predicted by ideal conditions in the table.
Gasoline20,0005,500Non-renewable. Oxidation of hydrocarbon: mass ofoxygen not included.Rocket fuel5,0001,300Non-renewable. Less than hydrocarbon becauseoxidizing agent forms part of fuelThermal3,8001,000Can be heated and reheated from renewable sources.graphiteTMES system graphite core @ 2500 K - does notinclude insulation/containment moduleLithium-ion350-500138Expensive, limited life, next generationbatteryFlywheels<400111Attractive, but still in early demonstrationNi—Cd battery170-20055Less expensive, limited life, toxic chemicals,significant weightLead-acid50-6016Less expensive, limited life, toxic chemicals, largebatteryweightSprings,<51.3Inexpensive, limited life, much less efficient methodRubber Bandsof energy storage than flywheel
To address the factor of an effective energy storage arrangement referred to above, it has been proposed to use graphite as a location flexible, high-density, long-life, environmentally responsible bulk energy storage medium for thermal energy sourced from both thermal and electrical supplies when such supply exceeds demand. An effective arrangement is disclosed in U.S. published application 2011/0289924 AI entitled High Density Energy Storage and Retrieval, the entire contents thereof is incorporated herein by reference. Energy stored in strategically located thermal-graphite systems may then be converted, via a host of available systems (broadly classified as heat engines which typically turn heat into mechanical motion necessary to drive electrical generators—such engines span from large supercritical steam turbines to small Stirling engines) to electrical energy on-demand, meeting electrical demand peaks and smoothing production drops typical of renewable generation, but also due to unexpected failures of conventional nuclear and hydrocarbon powered generating facilities. Nitrogen or an ideal gas mixture, as detailed in the above mentioned patent application, is used to draw energy from graphite which cannot contain any oxygen, since graphite will ignite in oxygen.
In addition to thermal-graphite energy storage systems, there are a host of energy storage systems available for both bulk, longer term storage (including pumped hydro, compressed air, and in some cases large-scale hydrogen fuel cell operations) and smaller, typically shorter term storage (including flywheels, batteries and other chemical storage systems including hydrogen fuel cells, and super-capacitors.
Unfortunately there remains the obvious requirement, common to all storage systems, for the critical provision of a suitable recharging period. Such period is effectively used when surplus energy (or the ability to generate such surplus energy on-demand) is available concurrently with suitable grid capacity to bring such surplus energy to the storage facility. Without such periods, storage systems are not recharged, and have less capacity to support the grid during times of low or zero renewable energy production. And unlike fossil fuels, when there is a shortage of renewable resources, there is no effective global transportation system which can move renewable energy to areas of need.
Today, grid-connected “spinning reserves” are maintained to fill these holes in supply which cannot be met by depleted renewable storage systems—the spinning reserves can be used to both stabilise grid voltages and recharge depleted storage systems. However, since such on-demand reserves are powered by fossil fuels, even with current fossil fuel global shipping operations, their availability in the future is uncertain in light of dwindling planetary fossil fuel reserves and increasing concerns about the air pollutants emitted during combustion of such fuels. Furthermore, powering spinning reserves with fossil fuels competes with the need for fossil fuels to be used for plastics and to power aircraft—both uses have no apparent substitutes and will thus pay whatever the cost to ensure priority supply.
In the absence of spinning reserves, many possible events, both predictable and unpredictable, reduce or eliminate critical storage recharging periods including:
1) Latitude dependent, seasonal reductions in solar and/or wind energy
2) Periodic prolonged periods of little or no wind or continued cloud
3) Massive storm centers which not only block solar energy, but exceed the wind tolerances of wind turbines, concurrently eliminating both forms of renewable energy
4) Environmental and equipment disasters leading to grid connectivity failures
5) Shortage of available land area for solar and/or wind installations of sufficient output to guarantee surplus charging periods
6) Failure of nuclear or other generation due to equipment breakdown or earthquake related events
7) Failure of grid infrastructure to expand with energy demand
8) Accelerated adoption of electric ground transportation—such vehicles, typically choosing to recharge at off-peak periods, reducing and possibly eliminating any available surplus
There remains a need for grid support in periods, and at specific places, where the reduction or elimination of such recharging periods renders local storage systems inoperative and leaves the renewable-powered grid unstable. Currently, the only commercially viable forms of long-distance transport of energy to power grids under such conditions are pipelines, railcars, and ships designed to move fossil fuels. The present invention in a preferred embodiment provides an effective system for the storage and transportation of energy and a system for on-demand global transportation of renewable energy with adaptive grid support capability.